Rechargeable batteries are electrochemical devices that can provide electricity by being discharged, and are able to be charged by storing electricity, e.g. produced by different energy sources, for later use. Thus, rechargeable batteries solve the problem of discontinuous production of electrical energy, especially when produced by renewable power sources like solar or wind, and allow for storing electrical energy when the electricity supply does not match the electricity demand.
Examples of rechargeable batteries are flow batteries or Li-ion batteries. Another example of rechargeable batteries may be metal air batteries such as Li-air batteries. These batteries are based on the use of the oxidation of a metal such as lithium at the anode and reduction of a gas such as oxygen at the cathode to induce a current flow. All such batteries have the disadvantage that the energy is stored in expensive metal atoms, and except for flow batteries, these atoms are stored in the electrodes where the electrochemical reactions occur, which limits the storage capacity and energy density.
Reversible fuel cells (RFCs) may also be used for electricity storage. RFCs, such as reversible solid oxide electrochemical cells (RSOECs), can be operated in electrolysis mode to convert electrical energy into fuel and in fuel cell mode to convert fuel into electrical energy. RFCs can thus operate in a similar manner as a flow battery. RFCs advantageously store energy in inexpensive hydrogen and hydrocarbon fuels which are stored outside of the cells. Metals are only used in the materials comprising the cells, to provide reaction sites where the electrochemical reactions occur. However, since RFCs operate with gases, they have the drawback of needing voluminous tanks or containers to store reactants and products, making their energy density low. Further, RFCs have a low efficiency compared with the batteries mentioned above.
CN 101540411 discloses a solid electrolyte direct carbon fuel cell where carbon fuel is filled in a tube-type battery. Once exhausted the carbon fuel needs to be refilled and carbon must be supplied by an external source.
JP 2010/003568 discloses a rechargeable direct carbon fuel cell where solid carbon is produced by thermal decomposition of hydrocarbon fuel. JP 2010/003568 discloses the use of parallel cells for continuous power generation. JP 2010/003568 discloses two cells connected in parallel, wherein the first cell supports solid carbon particles. Upon feeding oxygen gas, the first cell produces electricity and consumes carbon. Simultaneously with the power generation an organic compound is circulated in a passage in contact with the anode of the second cell where the organic compound decomposes so as to form solid carbon particles. When the carbon of the first cell is exhausted the circuit is switched so that the second cell becomes operative in the production of electricity. Ihara et al. (J. Electrochem. Soc. 2006, volume 153, pages 1544-1546) disclose a solid oxide fuel cell that uses solid carbon fuel supplied by the thermal decomposition of propane.
None of the fuel cells disclosed may be used as a rechargeable battery, i.e. may be used to store electrical energy.
The fuel cell of CN 101540411 needs to be re-supplied with solid carbon once the carbon is consumed so as to keep producing electricity. In the fuel cell of CN 101520411 carbon is not regenerated using electrical energy and to keep working the fuel cell needs to be opened and supplied with carbon from an external source.
The fuel cell of JP 2010/003568 allows for continuous power generation by switching the contacts between the different fuel cells. However, the fuel cell of JP 2010/003568 is not suitable for storing electrical energy. Ihara et al. uses thermal decomposition of propane to refill the solid oxide fuel cell so as to continue to produce electricity. However, the fuel cell of Ihara et al. is not suitable for storing electrical energy.
Hence, an improved rechargeable battery, i.e. a battery that can store a surplus of electrical energy would be advantageous, and in particular a rechargeable battery having higher energy density would be advantageous.
A more reliable and versatile rechargeable battery would also be advantageous, and in particular a rechargeable battery having a high round trip electrical energy storage efficiency would also be advantageous.